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Principal Air Routes Above 18,000 ft Near Long Valley, California

Explosive eruptions inject large amounts of volcanic ash and corrosive gases high into the atmosphere, especially into cruising altitudes used by commercial jet airplanes. Volcanic eruption clouds may drift for hundreds to thousands of kilometers from an erupting volcano, and can contaminate heavily used aeronautical routes over wide areas. Volcanic ash can damage aircraft flying surfaces and electronics, and cause engine failure. Eruption clouds also may cause flights to be diverted, delayed, or canceled.

Future explosive eruptions like those that occurred about 600 years ago from the Mono-Inyo Craters volcanic chain in the Long Valley area would generate eruption columns higher than 18,000 feet above sea level. The resulting eruption cloud would invade some of these air routes as far as several hundred kilometers downwind, depending on the size of the eruption and direction and speed of the prevailing wind. Airborne ash can diminish visibility, damage flight control systems, and cause jet engines to fail. Such an eruption would significantly affect air traffic over this part of the western United States.